molecules
Article
Formation of 5-Aminomethyl-2,3-dihydropyridine-4(1H)-ones
from 4-Amino-tetrahydropyridinylidene Salts
Werner Seebacher 1, * , Michael Hoffelner 1 , Ferdinand Belaj 2 , Teresa Pirker 3 , Muaaz Alajlani 4 ,
Rudolf Bauer 3 , Eva-Maria Pferschy-Wenzig 3 , Robert Saf 5 and Robert Weis 1
1
2
3
4
5
*
Pharmaceutical Chemistry, Institute of Pharmaceutical Sciences, University of Graz, Schubertstrasse 1,
8010 Graz, Austria
Institute of Chemistry, University of Graz, Schubertstrasse 1, 8010 Graz, Austria
Pharmacognosy, Institute for Pharmaceutical Sciences, University of Graz, Beethovenstrasse 8,
8010 Graz, Austria;
[email protected] (R.B.)
Faculty of Pharmacy, Al-Sham Private University, 011 Damascus, Syria;
[email protected]
Institute for Chemistry and Technology of Materials (ICTM), Graz University of Technology, Stremayrgasse 9,
8010 Graz, Austria
Correspondence:
[email protected]; Tel.: +43-316-380-5383; Fax: +43-316-380-9846
Abstract: Various 4-aminotetrahydropyridinylidene salts were treated with aldehydes in an alkaline
medium. Their conversion to 5-substituted β-hydroxyketones in a one-step reaction succeeded only
with an aliphatic aldehyde. Instead, aromatic aldehydes gave 5-substituted β-aminoketones or a
single δ-diketone. The new compounds were characterized using spectroscopic methods and a single
crystal structure analysis. Some of them showed anticancer and antibacterial properties.
Keywords: antibacterial; anticancer activity; dihydropyridin-4(1H)-ones; tetrahydropyridinylidene salts
Citation: Seebacher, W.;
1. Introduction
Hoffelner, M.; Belaj, F.; Pirker, T.;
Recently, we described the synthesis and antiprotozoal potency of
4-aminotetrahydropyridinylidene salts [1] and of 1-benzyl derivatives of these salts with
enhanced antiprotozoal activities [2,3]. The insertion of an additional benzyl group
in ring position 3 via alkylation under basic conditions yielded 1,3-disubstituted compounds with increased antiplasmodial activity [4]. This paper reports the synthesis of
5-substituted derivatives. Surprisingly, the reaction afforded mainly β-aminoketones, less
frequently δ-diketones or the expected β-hydroxyketones, which are usually obtained from
α,β-unsaturated ketones under Morita–Baylis–Hillmann conditions [5–7]. Similar Mannichlike products were obtained from formaldehyde and secondary amines with quinolin4(1H)-ones [8,9] or pyridin-4(1H)-ones [10,11]. However, their synthesis from 4-aminotetrahydropyridinylidene salts or from their hydrolysis products, the 2,3-dihydropyridin4(1H)-ones, have not yet been reported. Unsubstituted 2,3-dihydropyridin-4(1H)-one has
been prepared from ethyl 4-oxo-1,4-dihydropyridin-1-carboxylate [12]. Its 2,2-dimethyl
analog has been synthesized from 2-methylhexa-3,5-diyn-2-amine [13] as well as from
1-ethenyl-4,4-dimethylazetidin-2-one via UV-irradiation [14] (Scheme 1). Further cyclic
enaminones have been used as convenient synthons for numerous reactions including
photocycloadditions [15–19] and alkaloid synthesis [20]. The structural and electronic
properties of a series of 2,3-dihydropyridin-4-ones have been the subject of a theoretical
study [21]. So far, only the insertion of an allyl or an alkenyl substituent in ring position 5
of a dihydropyridine-4-one has been reported [22,23].
2,3-Dihydropyridin-4(1H)-one is a partial structure of cenocladamide, an alkaloid
from Piper cenocladum [24]. This alkaloid and derivatives thereof have previously been
investigated for their anticancer potency [25]. Furthermore, the dihydropyridin-4(1H)one moiety is part of derivatives of piperlongumine, which have been investigated for
Alajlani, M.; Bauer, R.;
Pferschy-Wenzig, E.-M.; Saf, R.; Weis,
R. Formation of 5-Aminomethyl-2,3dihydropyridine-4(1H)-ones from
4-Amino-tetrahydropyridinylidene
Salts. Molecules 2023, 28, 6869.
https://doi.org/10.3390/
molecules28196869
Academic Editor: Antal Csámpai
Received: 14 September 2023
Revised: 25 September 2023
Accepted: 27 September 2023
Published: 29 September 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Molecules 2023, 28, 6869. https://doi.org/10.3390/molecules28196869
https://www.mdpi.com/journal/molecules
Molecules 2023, 28, 6869
O
2 of 19
O
their anticancer activity [26] as well as of the potent antibacterial MRX-I [27] (Figure 1).
KOH,
MeOH,
r.t.
Therefore, we investigated the
new
compounds
for their anticancer activities as well as
N
N
their antibacterial potency in vitro.
H
COOC2H5
O
O
O
HN(CH
2)2, 100°C,
KOH, MeOH,
r.t.
1h
N
NH2
N
N
H
H
COOC2H5
O
O
UV-irradiation
)2, 100°C,
HN(CH
MeOH,240°C,
1h
200 min
N
NH2
N
H
O
O
UV-irradiation
N
MeOH, 40°C,
200 min
N
H
Scheme 1. Syntheses of 2,3-dihydropyridin-4(1H)-ones [12–14].
O
O
OCH3
N
N
R
OCH3
Piperlongumine-derivative
O
OH
O
Cenocladamide
O
H3CO
OCH3
OCH3
F
F
N
O
H3CO
O
H3CO
OH CO
N
3 H
N OH
N
N OCH
R
OCH3
N 3
O
Cenocladamide
Piperlongumine-derivative
F
MRX-1
F
F O
O
Figure 1. Compounds containing the 2,3-dihydropyridin-4(1H)-one motif [24–27].
2. Results and Discussion
O
2.1. Chemistry
N
N
O
H
N
N
O
F
The different 4-dialkylaminotetrahydropyridinylidene
salts 1a–1d
used as starting
They
were
exposed
for
several days
products were prepared as described
earlier
[1].
MRX-1
to aromatic aldehydes or aliphatic aldehydes in an alkaline medium at room temperature. Hydrolysis of 1a–1d in ring position 4 was taken into account, but the expected
β-hydroxyketones 11 and 12 were only formed as the main product from the aliphatic
cyclohexane carbaldehyde and pivalaldehyde, whereas the β-aminoketones 6a and 6b
ff
Molecules 2023, 28, 6869
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β
β
were isolated as by-products. The reaction of salts 1a–1d with aromatic aldehydes afforded
mainly
β-aminoketones
(compounds 2–5 and 7–10) (Scheme 2).
ff
β
Entry
R1, R2
1a
-(CH2)4-
1b
-(CH2)5-
1c
1d
-(CH2)2O(CH2)2H, t-Bu
R3
Ph
4F-C6H5
2-CF3C6H5
4-CF3C6H5
cyclohexyl
4-MeC6H5
4-isopropC6H5
4-pyridyl
propan-2-yl
t-Bu
Ph
4F-C6H5
2-CF3C6H5
4-CF3C6H5
cyclohexyl
Ph
4F-C6H5
Ph
Compounds
2a
3a
4a
5a
6a, 11
7a
8a
9a
10a
12
2b
3b
4b
5b
6b, 11
2c
3c
2d
Yield * 2–10 (%)
68
84
24
37
4 (40 **)
45
6 (67 **)
9 (15 **)
16 (47 **)
50
55
57
54
9 (41 **)
77
32
27
Yield * 11, 12 (%)
19 (36 **)
68
23 (32 **)
-
* Yields after crystallization. (**) Yields calculated from proton NMR spectra of raw products.
Scheme 2. Synthesis of compounds 2–12.
Due to the low solubility in water of solid ferrocenyl carbaldehyde and 4-ethoxy3-methoxybenzaldehyde, ethanol was added to the reaction mixture. Other than the so
far reported reactions, these electron-sufficient
aldehydes resulted in dimers 13 and 14
ffi
(Scheme 3).
In order to confirm the initial steps of the proposed mechanism, we treated the
4-dialkylaminotetrahydropyridinylidene salt 1a with potassium hydroxide for 4 days to
yield dihydropyridone 15, quantitatively. Then, a mixture of pyrrolidine and benzaldehyde
in alkaline solution was added and considerable amounts of 2a were formed overnight. The
reaction of 15 without secondary amine resulted in a high yield of the hydroxy analog 11
(Scheme 4).
Molecules 2023, 28, 6869
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H
N
MeO
O
MeO
EtO
1a or 1b
1a or 1b
OH
EtO
2
3
H r.t., 5d
KOH, H2O, EtOH (1:2),
H2
N3
1
6
1
6 4
5
4
5
O
KOH, H2O, EtOH (1:2), r.t., 5d
O
OEt
O
O
5'
NH
2'
OMe
OMe
5'
4'
3' 6'
2'
4'
3'
OEt
6'
NH
1'
1'
13
13
28% from 1a
28% from
62%1afrom 1b
62% from 1b
FeFe
1a
1a
CHO
CHO
H
N
6
H
N
2
3
1
2
5
43
4
1
O
KOH, H2O, EtOH (1:2), r.t., 5d
KOH, H2O, EtOH (1:2), r.t., 5d
58%
58%
O
3'
O
4'
Fe
6Fe
5
O5'
5'
6'
4'
2' 3'
NH
1' 2'
14
NH
1'
14
δ δ-diketones 13 and 14 with electron-sufficient
ffi
Scheme 3. Synthesis of
aldehydes.
δ
ffi
Scheme 4. Control experiments with dihydropyridone 15.
6'
Molecules 2023, 28, 6869
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The reaction mechanism can be considered as follows:
The
4-dialkylaminotetrahydropyridinylidene salts 1 are deprotonated by potassium hydroxide to their corresponding bases 16 in the first step. Due to strong alkaline conditions,
these are hydrolyzed to ketone 15 which is deprotonated to the resonance-stabilized anattacked by aldehydes resulting in
ion 17. The formed methylene component is readily
tt
aldols 18,19. If R3 is an aliphatic group, tautomerization to compounds 11,12 may occur.
of aldols 18,19. Cleavage of a
Moreover, a proton can be abstracted from the α-position
α
hydroxy group from the formed resonance-stabilized anions 20,21 leads to α,β-unsaturated
αβ
ketones 22,23. Addition of secondary amines in β-position yields β-aminoketones
2–10.
β
β
This is the main reaction for the less electrophilic aromatic aldehydes as well as isobutyric aldehydes. Alternatively, compounds 22,23 can be attacked by anion
tt 17 resulting in
δ-diketones 13, δ14 via a Michael reaction (Scheme 5).
Scheme 5. Possible mechanisms of the formation of compounds 2–14.
2.2. Structure Elucidation
The structures of the obtained compounds were elucidated using NMR spectroscopy:
In the 13 C-spectra, a signal shift from 162 to 189 ppm was observed for C-4 due to ketone
formation. Furthermore, the resonance of the proton in position 5 disappeared in the 1 H
spectra. The remaining olefinic proton showed a coupling to the proton in ring position 1.
Connectivity was proven by cross peaks of the newly formed methine proton to C-4 and C-5
as well as to NCH2 and aromatic carbons in the HMBC spectra. Through-space couplings
were detected in NOE experiments (Nuclear Overhauser experiments) (Figure 2). Both can
be seen in the Supplementary Materials.
Molecules 2023, 28, 6869
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Figure 2. Through-space couplings indicated as arrows in compound 2a.
Finally, evidence of the structure of compound 6a was achieved using a single X-ray
crystal analysis which confirmed the compound as 5-[cyclohexyl(pyrrolidin-1-yl)methyl]2,2-dimethyl-2,3-dihydropyridin-4(1H)-one. This is the first determination of a structure
containing a (pyrrolidin-1-yl) substituent in a 2,3-dihydropyridin-4(1H)-one (Figure 3). All
atoms lie on general positions. The compound is a racemate.
Figure 3. Stereoscopic ORTEP [28] plot of 6a showing the atomic numbering scheme. The probability
ellipsoids are drawn at the 50% probability level. The H atoms are drawn with arbitrary radii.
Nitrogen atoms are blue, oxygen atoms are red.
2.3. Biological Activities
Most of the new compounds were tested for their anti-proliferative activity against
human leukemia cells (CCRF-CEM) as well as against non-tumorigenic human lung fibroblasts (MRC-5) using an XTT assay. Cells were exposed to compounds at concentrations of 5
and 50 µM for a time period of 72 h. The results are presented in Figure 4A,B.
At concentrations of 5 µM, only the 2-(trifluoromethyl)phenyl aminoketone 4a showed
moderate activity against a leukemia cell line. All other test compounds were inactive
at this concentration. At 50 µM, the (tert-butylamino)ketone 2d as well as the dimer 11
were still non-effective and the 4-(trifluoromethyl)phenyl aminoketones 5a and 5b had
moderate activity. All other compounds showed a selective anti-leukemic effect. However,
the aminoketones 6b and 8a, dimer 12, and the β-hydroxyketone 13 were comparably
toxic against lung fibroblasts. The most promising selectivity was observed for the 2(trifluoromethyl)phenyl aminoketone 4a, which showed good anti-leukemic effect paired
with low cytotoxicity in fibroblasts at 5 µM.
Molecules 2023, 28, 6869
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Figure 4. Anti-proliferative activity of compounds 2b–14 against human leukemia cell line CCRFCEM (A) and against non-tumorigenic MRC-5 lung fibroblasts (B) expressed as mean ± SEM. Cells
were treated with 50 and 5 µM of the compounds for 72 h. Cell viability was measured via XTT
assay. Viability rates were expressed as a percentage of vehicle-treated control cells (0.1% DMSO).
Vinblastine (VB) at a concentration of 100 nM served as positive control.
The results of the antibacterial assay against Gram-negative (E. coli) and Gram-positive
bacteria (B. sub.) are listed in Table 1.
ff
Table 1. Antibacterial activity of compounds 2b–14.
ff
β
Substance
Escherichia coli
Bacillus subtilis
2b
+*
-
+
+
2c ff
3a
++
-
3b
+
+
3c
+
-
4a
±
+
4b
++
±
5a
++
+
5b
++
+
6a
++
±
6b
+
±
7a
+
+
8a
+
-
9a
+
-
11
+
++
13
+
+
14
±
±
* Antimicrobial activity monitored as mild/detectable activity (±); active (+); higher activity (++); no activity (-).
Molecules 2023, 28, 6869
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The most active compounds against Escherichia coli were aminoketones 3a, 4b, 5a, and
5b with fluorophenyl or (trifluoromethyl)phenyl substitution as well as their cyclohexyl
analog 6a. The most active compound against Bacillus subtilis was the β-hydroxyketone 11.
3. Materials and Methods
3.1. Instrumentation and Chemicals
Solvents were used without further purification. Aldehydes were purified via chromatographic separation on a small column filled with aluminum oxide 60 active basic
(activity I) (Merck, Darmstadt, Germany) to remove acidic impurities. For thin-layer chromatography (TLC), TLC plates with silica gel 60 F254 (Merck, Darmstadt, Germany) were
used. Melting points were obtained on an Electrothermal IA 9200 melting point apparatus.
IR spectra: Bruker Alpha Platinum ATR FTIR spectrometer (KBr discs); frequencies are
reported in cm−1 . The structures of all newly synthesized compounds were determined
using one- and two-dimensional NMR spectroscopy. The NMR spectra were acquired with
Varian UnityInova 400 (298 K) or Bruker Avance Neo 400 instruments in 5 mm tubes. Some
spectra were acquired in CDCl3 containing 0.03% TMS. Chemical shifts were recorded
in parts per million (ppm). For the 1 H spectra, TMS (0.00) was used as the internal standard, and for the 13 C spectra, the central peak of the CDCl3 peak was used as the internal
reference (77.0). Most of the spectra were acquired in DMSO-d6 . In this case, the central
peaks of the solvent signal at 2.49 ppm in the 1 H spectra and at 39.7 ppm in the 13 C spectra served as the internal references. Shifts in the 1 H NMR (400 MHz) and the 13 C NMR
(100 MHz) spectra are reported in ppm; 1 H- and 13 C-resonances were assigned using 1 H,1 Hand 1 H,13 C-correlation spectra and are numbered as given in Scheme 1. Abbreviations:
aromatic H, ArH; aromatic C, ArC; and quaternary aromatic C, ArCq . Signal multiplicities
are abbreviated as follows: s, singlet; d, doublet; dd, double doublet; dsept, double septet;
quin, quintet; t, triplet; m, multiplet; and br, broad. Coupling constants (J) are reported in
Hertz (Hz). Assignments marked with an asterisk are interchangeable. HRMS: Micromass
Tofspec 3E spectrometer (MALDI) and GCT Premier (Waters, Milford, MA, USA) (EI, 70 eV)
or Q Exactive Hybrid Quadrupole-Orbitrap mass spectrometer, Thermo Fisher Scientific,
Austin, TX, USA (HESI, capillary voltage 3.5 kV). Electron ionization (EI+, 70 eV, source
at 250 ◦ C) mass spectra were acquired on a JMS-T2000GC (AccuTOFTM GC-Alpha) from
JEOL Ltd. (Tokyo, Japan) equipped with a direct insertion probe (DIP). The 1 H NMR and
13 C NMR spectra of new compounds are provided in the Supplementary Materials.
3.2. Syntheses
Compounds 1a–1d were prepared earlier and their NMR data are in accordance with
the reported literature [1].
rac-2,2-Dimethyl-5-[(R)-phenyl(pyrrolidin-1-yl)methyl]-2,3-dihydropyridin-4(1H)-one
(2a): Compound 1a (2.000 g (6.53 mmol)) was suspended in water (16 mL) and a solution
of KOH (1.466 g (26.13 mmol)) in water (16 mL) was added. The mixture was stirred at r.t.
until a solution was formed (ca. 5–10 min). Then, benzaldehyde (0.693 g (6.53 mmol)) was
added. The reaction mixture was stirred for 4 days at r.t. The separated crystalline solid
was filtered with suction, washed with water and acetone, and dried in vacuo yielding
2a (1.261g (68%)) as an orange-yellow solid. For analytical purposes, it was recrystallized
from ethyl acetate/cyclohexane resulting in a white solid.
From 15: Compound 15 (0.671 g (5.36 mmol)) was dissolved in a solution of KOH
(1.213 g (21.62 mmol)) in distilled water (26 mL). The mixture was sonicated and stirred
at r.t. until all was dissolved. To the resulting solution, pyrrolidine (0.409 g (5.75 mmol))
and benzaldehyde (0.582 g (5.48 mmol)) were added. The reaction mixture was stirred for
16 h at r.t. The separated crystalline solid was filtered with suction, washed clean with
water, and dried in vacuo resulting in 2a (1.129 g (74%)) as a pale pink solid. For analytical
purposes, it was recrystallized from ethyl acetate resulting in colorless needles.
Rf (CH2 Cl2 :MeOH = 10:1): 0.09; mp: 147–148 ◦ C; IR = 3232, 2967, 2783, 1623, 1568,
1534, 1395, 1231, 700; 1 H NMR (CDCl3 , 400 MHz) δ = 1.19 (s, 3H, CH3 ), 1.29 (s, 3H, CH3 ),
Molecules 2023, 28, 6869
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1.75 (br, s, 4H, (CH2 )2 ), 2.37 (s, 2H, 3-H), 2.50 (br, s, 4H, 2NCH2 ), 4.52 (s, 1H, 1′ -H), 4.60 (d,
J = 5.5 Hz, 1H, 1-H), 7.14–7.38 (m, 6H, 6-H, ArH); 13 C NMR (CDCl3 , 100 MHz) δ = 23.49
((CH2 )2 ), 26.57, 27.57 (2CH3 ), 49.18 (C-3), 53.17 (2NCH2 ), 53.80 (C-2), 63.98 (C-1′ ), 111.43
(C-5), 126.09, 127.14, 128.03 (5ArC), 144.87 (ArCq ), 149.23 (C-6), 189.50 (C-4); HRMS (EI):
calcd. (C18 H24 N2 O+ ) [M]+ : 284.1889; found: 284.1874.
rac-2,2-Dimethyl-5-[(R)-phenyl(piperidin-1-yl)methyl]-2,3-dihydropyridin-4(1H)-one
(2b): Compound 1b (2.091 g (6.53 mmol)) was suspended in water (16 mL) and a solution
of KOH (1.470 g (26.20 mmol)) in water (16 mL) was added. The mixture was stirred at r.t.
until a solution was formed (ca. 10–20 min). Then, benzaldehyde (0.695 g (6.55 mmol)) was
added. The reaction mixture was stirred for 5 days at r.t. The separated crystalline solid
was filtered with suction, washed with water and acetone, and dried in vacuo resulting in
2b (0.972 g (50%)) as an orange-yellow solid. For analytical purposes, it was recrystallized
from ethyl acetate resulting in a white solid. Rf (CH2 Cl2 :MeOH = 1:1): 0.86; mp: 158 ◦ C;
IR = 2925, 1623, 1571, 1527, 1255, 1232, 700; 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.09 (s, 3H,
CH3 ), 1.18 (s, 3H, CH3 ), 1.31–1.51 (m, 6H, (CH2 )3 ), 2.13–2.22 (m, 4H, 3-H, NCH2 ), 2.28–2.38
(m, 2H, NCH2 ), 4.37 (s, 1H, 1′ -H), 6.95 (d, J = 6.8 Hz, 1H, 6-H), 7.09–7.14 (m, 1H, ArH),
7.20–7.26 (m, 4H, ArH), 7.35 (d, J = 6.8 Hz, 1H, 1-H); 13 C NMR (DMSO-d6 , 100 MHz) δ
24.62 (CH2 ), 26.11 (2CH2 ), 26.19, 26.78 (2CH3 ), 48.90 (C-3), 52.34 (2NCH2 ), 53.03 (C-2), 64.17
(C-1′ ), 106.75 (C-5), 125.98, 127.30, 128.17 (5ArC), 144.62 (ArCq ), 149.38 (C-6), 188.49 (C-4);
HRMS (HESI): calcd. (C19 H27 N2 O+ ) [M + H]+ : 299.2123; found: 299.2114.
rac-2,2-Dimethyl-5-[(R)-phenyl(morpholin-4-yl)methyl]-2,3-dihydropyridin-4(1H)-one
(2c): Compound 1c (2.000 g (6.22 mmol)) was suspended in water (30 mL) and KOH
(1.397 g (24.89 mmol)) was added. To the resulting yellow solution benzaldehyde (0.660 g
(6.22 mmol)) was added. The reaction mixture was stirred for 4 days at r.t. The separated
crystalline solid was filtered with suction, washed with water and acetone, and dried over
phosphorus pentoxide in vacuo resulting in 2c (1.436 g (77%)) as an off-white solid. For
analytical purposes, it was recrystallized from ethyl acetate resulting in white needles.
Rf (CH2 Cl2 :MeOH = 1:1): 0.89; mp: 165 ◦ C; IR = 3257, 2961, 1623, 1571, 1522, 1395, 1291,
1231, 1181, 1116, 702; 1 H NMR (DMSO-d6 , 400 MHz) δ 1.09 (s, 3H, CH3 ), 1.17 (s, 3H, CH3 ),
2.15–2.25 (m, 4H, 3-H, NCH2 ), 2.29–2.39 (s, 2H, NCH2 ), 3.49–3.60 (br, s, 4H, 2OCH2 ), 4.36
(s, 1H, 1′ -H), 7.00 (d, J = 6.8 Hz, 1H, 6-H), 7.13–7.16 (m, 1H, ArH), 7.25–2.26 (m, 4H, ArH),
7.42 (d, J = 6.8 Hz, 1H, 1-H); 13 C NMR (DMSO-d6 , 100 MHz) δ 26.20, 26.77 (2CH3 ), 48.82
(C-3), 52.11 (2NCH2 ), 53.04 (C-2), 64.25 (C-1′ ), 66.61 (2OCH2 ), 106.04 (C-5), 126.26, 127.42,
128.33 (5ArC), 143.71 (ArCq ), 149.51 (C-6), 188.47 (C-4); HRMS (HESI): calcd. (C14 H16 ON+ )
[M + H − C4 H9 NO]+ : 214.1232; found: 214.1223.
rac-5-[(R)-(tert-Butylamino)(phenyl)methyl]-2,2-dimethyl-2,3-dihydropyridin-4(1H)one (2d): Compound 1d (2.013 g (6.53 mmol)) was suspended in water (30 mL) and
KOH (1.400 g (25 mmol)) was added. Then, benzaldehyde (0.693 g (6.53 mmol)) was added
and the reaction mixture was stirred for 6 days at r.t. From the resulting orange resin, the
aqueous solution was decanted and the resin was washed with water repeatedly. Then,
it was dried overnight in vacuo over phosphorus pentoxide. The dry resin was dissolved
in the minimum amount of hot ethyl acetate and left for crystallization at r.t. The solid
was sucked off and dried resulting in 2d (0.512 g (27%)) as off-white needles. Rf (MeOH):
0.07; mp: 136 ◦ C; IR = 2964, 1633, 1550, 1477, 1454, 1412, 1367, 1357, 1195, 1174, 947, 875,
828, 727, 713, 697, 678; 1 H NMR (DMSO-d6 , 400 MHz) δ 1.07 (s, 3H, CH3 ), 1.10 (s, 3H,
CH3 ), 1.20 (s, 9H 3CH3 ), 2.31 (d, J = 15.0 Hz, 1H, 3-H), 2.36 (d, J = 15.0 Hz, 1H, 3-H), 5.21
(s, 1H, 1′ -H), 5.98 (br, s, 1H, NH*), 6.25 (br, s, 1H, 6-H*), 6.94 (br, s, 1H, 1-H*), 7.12–7.34 (m,
5H, ArH); 13 C NMR (DMSO-d6 , 100 MHz) δ 26.64, 26.81 (2CH3 ), 31.66 (3CH3 ), 41.37 (C-3),
50.97 (C-2), 53.45 (C(CH3 )3 ), 73.61 (C-1′ ), 109.18 (C-5), 126.17, 126.43, 127.59 (5ArC), 138.93
(C-6), 146.02 (ArCq ), 161.70 (C-4); HRMS (HESI): calcd. (C18 H27 N2 O+ ) [M + H]+ : 287.2123;
found: 287.2114.
rac-5-[(R)-(4-Fluorophenyl)(pyrrolidin-1-yl)methyl]-2,2-dimethyl-2,3-dihydropyridin4(1H)-one (3a): Compound 1a (2.000 g (6.53 mmol)) was suspended in water (16 mL) and
a solution of KOH (1.466 g (26.13 mmol)) in water (16 mL) was added. The mixture was
Molecules 2023, 28, 6869
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stirred at r.t. until a solution was formed (ca. 5–10 min). Then, 4-fluorobenzaldehyde
(0.810 g (6.53 mmol)) was added and the reaction mixture was stirred for 6 days at r.t.
The separated crystalline solid was filtered with suction, washed with water, and dried in
vacuo over phosphorus pentoxide resulting in 3a (1.658 g (84%)) as a beige solid. It was
recrystallized from ethyl acetate resulting in white needles. Rf (CH2 Cl2 :MeOH = 1:1): 0.29;
mp: 169 ◦ C; IR = 3231, 2970, 2783, 1623, 1603, 1568, 1531, 1507, 1395, 1220, 1182; 1 H NMR
(DMSO-d6 , 400 MHz) δ 1.07 (s, 3H, CH3 ), 1.16 (s, 3H, CH3 ), 1.62–1.65 (m, 4H, (CH2 )2 ), 2.14
(s, 2H, 3-H), 2.25–2.39 (m, 2H, NCH2 ), 2.33–2.39 (m, 2H, NCH2 ), 4.29 (s, 1H, 1′ -H), 7.00–7.05
(m, 2H, ArH), 7.10 (d, J = 6.8 Hz, 1H, 6-H), 7.25–7.29 (m, 2H, ArH), 7.36 (d, J = 6.8 Hz, 1H,
1-H); 13 C NMR (DMSO-d6 , 100 MHz) δ 23.34 ((CH2 )2 ), 26.02, 26.85 (2CH3 ), 48.92 (C-3),
52.79 (2NCH2 ), 53.03 (C-2), 63.35 (C-1′ ), 108.89 (C-5), 114.74 (d, 2 J(C,F) = 21.0 Hz, ArC),
128.66 (d, 3 J(C,F) = 7.9 Hz, ArC), 141.72 (d, 4 J(C,F) = 3.1 Hz, ArCq ), 149.08 (C-6), 160.69 (d,
1 J(C,F) = 241.3 Hz, ArC ), 187.86 (C-4); HRMS (HESI): calcd. (C H FN O+ ) [M + H]+ :
q
18 24
2
303.1873; found: 303.1863.
rac-5-[(R)-(4-Fluorophenyl)(piperidin-1-yl)methyl]-2,2-dimethyl-2,3-dihydropyridin4(1H)-one (3b): Compound 1b (2.091 g (6.53 mmol)) was suspended in water (30 mL) and
KOH (1.470 g (26.20 mmol)) was added. Then, 4-fluorobenzaldehyde (0.810 g (6.53 mmol))
was added and the reaction mixture was stirred for 4 days at r.t. The separated crystalline
solid was filtered with suction, washed with water, and dried in vacuo over phosphorus
pentoxide yielding 3b as a yellowish solid. It was dissolved in hot ethyl acetate and the
insoluble part was removed via filtration. The product crystallized overnight as needles,
was sucked off, and washed with ice-cold ethyl acetate resulting in 3b (1.137 g (55%))
as yellowish needles. Rf (CH2 Cl2 :MeOH = 1:1): 0.30; mp: 183 ◦ C; IR = 3250, 3031, 2965,
2938, 1624, 1571, 1525, 1506, 1393, 1380, 1290, 1255, 1231, 1220, 1180; 1 H NMR (DMSO-d6 ,
400 MHz) δ 1.10 (s, 3H, CH3 ), 1.18 (s, 3H, CH3 ), 1.34–1.48 (m, 6H, (CH2 )3 ), 2.14–2.23 (m, 4H,
3-H, NCH2 ), 2.26–2.36 (m, 2H, NCH2 ), 4.37 (s, 1H, 1′ -H), 6.95 (d, J = 6.8 Hz, 1H, 6-H), 7.05
(t, J = 8.9 Hz, 2H, ArH), 7.25 (dd, J = 8.5, 5.8 Hz, 2H, ArH), 7.38 (d, J = 6.8 Hz, 1H, 1-H); 13 C
NMR (DMSO-d6 , 100 MHz) δ = 24.56 (CH2 ), 26.09 (2CH2 ), 26.15, 26.72 (2CH3 ), 48.88 (C-3),
52.22 (2NCH2 ), 53.02 (C-2), 63.60 (C-1′ ), 106.41 (C-5), 114.78 (d, 2 J(C,F) = 21.0 Hz, ArC),
128.96 (d, 3 J(C,F) = 7.8 Hz, ArC), 140.55 (d, 4 J(C,F) = 3.0 Hz, ArCq ), 149.31 (C-6), 160.66
(d, 1 J(C,F) = 241.6 Hz, ArCq ), 188.51 (C-4); HRMS (HESI): calcd. (C19 H26 FN2 O+ ) [M + H]+ :
317.2029; found: 317.2020.
rac-5-[(R)-4-Fluorophenyl)(morpholin-4-yl)methyl]-2,2-dimethyl-2,3-dihydropyridin4(1H)-one (3c): Compound 1c (0.700 g (2.18 mmol)) was suspended in water (11 mL) and
KOH (0.489 g (8.71 mmol)) was added. 4-Fluorobenzaldehyde (0.271 g (2.18 mmol)) was
added and the reaction mixture was stirred for 6 days at r.t. The separated resin was
washed with water and dried in vacuo. It was triturated with hot ethyl acetate and the
insoluble parts were filtered off and a part of the solvent was removed via evaporation. The
formed amorphous precipitate was filtered off and the filtrate concentrated in vacuo. The
product crystallized and was sucked off, washed with cold ethyl acetate, and dried yielding
3c (0.225 g (32%)). Rf (CH2 Cl2 :MeOH = 1:1): 0.90; mp: 162 ◦ C; IR = 3244, 2969, 2957, 2842,
2809, 1651, 1621, 1571, 1508, 1394, 1292, 1263, 1249, 1224, 1182, 1118; 1 H NMR (DMSO-d6 ,
400 MHz) δ = 1.09 (s, 3H, CH3 ), 1.17 (s, 3H, CH3 ), 2.14–2.23 (m, 4H, 3-H, NCH2 ), 2.30–2.39
(m, 2H, NCH2 ), 3.51–3.56 (m, 4H, 2OCH2 ), 4.35 (s, 1H, 1′ -H), 7.00 (d, J = 6.8 Hz, 1H, 6-H),
7.07 (t, J = 8.8 Hz, 2H, ArH), 7.27 (dd, J = 8.5, 5.8 Hz, 2H, ArH), 7.45 (d, J = 6.8 Hz, 1H,
1-H); 13 C NMR (DMSO-d6 , 100 MHz) δ = 26.18, 26.73 (2CH3 ), 48.82 (C-3), 52.02 (2NCH2 ),
53.05 (C-2), 63.72 (C-1′ ), 66.60 (2OCH2 ), 105.78 (C-5), 114.99 (d, 2 J(C,F) = 21.0 Hz, ArC),
129.15 (d, 3 J(C,F) = 7.7 Hz, ArC), 139.72 (d, 4 J(C,F) = 3.0 Hz, ArCq ), 149.46 (C-6),
160.81 (d, 1 J(C,F) = 241.8 Hz, ArCq ), 188.51 (C-4); HRMS (HESI): calcd. (C14 H15 FNO+ )
[M + H − C4 H9 NO]+ : 232.1138; found: 232.1129.
rac-2,2-Dimethyl-5-{(R)-(pyrrolidin-1-yl)[(2-trifluoromethyl)phenyl]methyl}-2,3dihydropyridin-4(1H)-one (4a): Compound 1a (1.000 g (3.27 mmol)) was suspended in
water (16 mL) and KOH (0.733 g (13.1 mmol)) was added. The mixture was stirred at
r.t. until a solution was formed (ca. 5–10 min). Then, 2-(trifluoromethyl)benzaldehyde
Molecules 2023, 28, 6869
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(0.569 g (3.27 mmol)) was added and the reaction mixture was stirred for 4 days at r.t. The
separated resinous solid was washed with water and dried in vacuo over phosphorus
pentoxide. It was dissolved in hot ethyl acetate and cyclohexane was added until the
first turbidity appeared. An oil separated which solidified. This amorphous precipitate
was filtered off and discarded. The filtrate was evaporated and dissolved in hot ethyl
acetate. It was allowed to stand for some days until crystallization took place resulting in
4a (0.282 g (24%)) as white needles. Rf (CH2 Cl2 :MeOH = 1:1): 0.39; mp: 139 ◦ C; IR = 3281,
2968, 1623, 1606, 1577, 1530, 1392, 1311, 1262, 1158, 1124, 1034, 773; 1 H NMR (DMSO-d6 ,
400 MHz) δ = 1.08 (s, 3H, CH3 ), 1.14 (s, 3H, CH3 ), 1.58–1.67 (m, 4H, (CH2 )2 ), 2.12–2.21 (m,
2H, 3-H), 2.28–2.46 (m, 4H, 2NCH2 ), 4.81 (s, 1H, 1′ -H), 6.70 (d, J = 6.9 Hz, 1H, 6-H), 7.25
(d, J = 6.9 Hz, 1H, 1-H), 7.38 (t, J = 7.6 Hz, 1H, ArH), 7.60 (d, J = 7.9 Hz, 1H, ArH), 7.64
(t, J = 7.6 Hz, 1H, ArH), 8.04 (d, J = 7.8 Hz, 1H, ArH); 13 C NMR (DMSO-d6 , 100 MHz)
δ = 23.31 ((CH2 )2 ), 26.33, 26.74 (2CH3 ), 48.89 (C-3), 52.05 (2NCH2 ), 52.95 (C-2), 57.93
(C-1′ ), 107.40 (C-5), 124.46 (q, 1 J(C,F) = 274 Hz, CF3 ), 125.93 (q, 3 J(C,F) = 6.1 Hz, ArC),
125.99 (q, 2 J(C,F) = 29.5 Hz, ArCq ), 126.68 (ArC), 129.67 (ArC), 132.26 (ArC), 143.16
(ArCq ), 149.61 (C-6), 187.94 (C-4); HRMS (HESI): calcd. (C19 H24 F3 N2 O+ ) [M + H]+ :
353.1841; found: 353.1830.
rac-2,2-Dimethyl-5-{(R)-(piperidin-1-yl)[(2-trifluoromethyl)phenyl]methyl}-2,3dihydropyridin-4(1H)-one (4b): Compound 1b (2.091 g (6.53 mmol)) was suspended in water (30 mL) and KOH (1.400 g (25 mmol) was added. Then, 2-(trifluoromethyl)benzaldehyde
(1.137 g (6.53 mmol)) was added and the reaction mixture was stirred for 5 days at r.t. It was
poured into a separatory funnel and was extracted 5 times with CH2 Cl2 . The combined
organic phases were dried over sodium sulfate, filtered, and the solvent was evaporated.
The orange resinous residue was dissolved in the minimum amount of hot ethyl acetate
and left for crystallization over the weekend. The precipitate was sucked off, washed with
cold ethyl acetate, and dried at 100 ◦ C in vacuo resulting in 4b (1.370 g (57%)) as a white
powder. Rf (CH2 Cl2 :MeOH = 1:1): 0.83; mp: 168 ◦ C; IR = 2922, 1626, 1575, 1531, 1451, 1386,
1311, 1295, 1266, 1247, 1162, 1153, 1112, 1087, 1058, 1034; 1 H NMR (DMSO-d6 , 400 MHz)
δ = 1.06 (s, 3H, CH3 ), 1.14 (s, 3H, CH3 ), 1.27–1.50 (m, 6H, (CH2 )3 ), 2.09–2.28 (m, 4H, 3-H,
NCH2 ), 2.30–2.40 (m, 2H, NCH2 ), 4.75 (s, 1H, 1′ -H), 6.62 (d, J = 6.8 Hz, 1H, 6-H), 7.27 (d,
J = 6.9 Hz, 1H, 1-H), 7.36 (t, J = 7.6 Hz, 1H, ArH), 7.60 (d, J = 7.9 Hz, 1H, ArH), 7.63 (t,
J = 7.6 Hz, 1H, ArH), 8.05 (d, J = 7.9 Hz, 1H, ArH); 13 C NMR (DMSO-d6 , 100 MHz)
δ = 24.60 (CH2 ), 26.17 (2CH2 ), 26.58 (2CH3 ), 48.81 (C-3), 52.14 (2NCH2 ), 52.94 (C-2), 59.18
(C-1′ ), 105.58 (C-5), 124.49 (q, 1 J(C,F) = 274 Hz, CF3 ), 125.98 (q, 3 J(C,F) = 6.0 Hz, ArC),
126.65 (ArC), 126.73 (q, 2 J(C,F) = 29.4 Hz, ArCq ), 129.13 (ArC), 132.26 (ArC), 143.57 (ArCq ),
149.81 (C-6), 188.42 (C-4); HRMS (HESI): calcd. (C20 H26 F3 N2 O+ ) [M + H]+ : 367.1997;
found: 367.1986.
rac-2,2-Dimethyl-5-{(R)-(pyrrolidin-1-yl)[(4-trifluoromethyl)phenyl]methyl}-2,3dihydropyridin-4(1H)-one (5a): Compound 1a (2.000 g (6.53 mmol)) was suspended in
water (30 mL) and KOH (1.400 g (25 mmol)) was added. The mixture was stirred at r.t.
until a solution was formed (ca. 5–10 min). Then, 4-(trifluoromethyl)benzaldehyde (1.137 g
(6.53 mmol)) was added. The reaction mixture was stirred for 7 days at r.t. It was poured
into a separatory funnel and extracted 5 times with CH2 Cl2 . The combined organic phases
were dried over sodium sulfate, filtered, and the solvent was evaporated. The orange
resinous residue was dissolved in the minimum amount of hot ethyl acetate and left for
crystallization overnight. The solid was sucked off and washed with cold ethyl acetate
and dried at 100 ◦ C in vacuo resulting in 5a (0.856 g (37%)) as yellowish needles. Rf
(CH2 Cl2 :MeOH = 1:1): 0.45; mp: 167 ◦ C; IR = 2967, 1568, 1532, 1259, 1391, 1324, 1226, 1151,
1113, 1104, 1064, 1015, 906, 665; 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.07 (s, 3H, CH3 ), 1.16
(s, 3H, CH3 ), 1.62–1.69 (m, 4H, (CH2 )2 ), 2.11–2.19 (m, 2H, 3-H), 2.26–2.33 (m, 2H, NCH2 ),
2.35–2.41 (m, 2H, NCH2 ), 4.40 (s, 1H, 1′ -H), 7.11 (d, J = 6.8 Hz, 1H, 6-H), 7.45 (d, J = 6.7 Hz,
1H, 1-H), 7.47 (d, J = 8.1 Hz, 2H, ArH), 7.58 (d, J = 8.1 Hz, 2H, ArH); 13 C NMR (DMSO-d6 ,
100 MHz) δ = 23.36 ((CH2 )2 ), 25.98, 26.84 (2CH3 ), 48.82 (C-3), 52.73 (2NCH2 ), 53.07 (C-2),
63.78 (C-1′ ), 108.22 (C-5), 124.61 (q, 1 J(C,F) = 272 Hz, CF3 ), 125.10 (q, 3 J(C,F) = 3.8 Hz, ArC),
Molecules 2023, 28, 6869
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126.78 (q, 2 J(C,F) = 31.5 Hz, ArCq ), 127.62 (ArC), 149.36 (C-6), 150.40 (ArCq ), 187.82 (C-4);
HRMS (HESI): calcd. (C19 H24 F3 N2 O+ ) [M + H]+ : 353.1841; found: 353.1830.
rac-2,2-Dimethyl-5-{(R)-(piperidin-1-yl)[(4-trifluoromethyl)phenyl]methyl}-2,3dihydropyridin-4(1H)-one (5b): Compound 1b (2.091 g (6.53 mmol)) was suspended in water (30 mL) and KOH (1.400 g (25 mmol)) was added. Then, 2-(trifluoromethyl)benzaldehyde
(1.137 g (6.53 mmol)) was added and the reaction mixture was stirred for 7 days at r.t. It was
poured into a separatory funnel and extracted 5 times with CH2 Cl2 . The combined organic
phases were dried over sodium sulfate, filtered, and the solvent was evaporated. The
orange resin was dissolved in the minimum amount of hot ethyl acetate and left for crystallization overnight. The solid was sucked off, washed with cold ethyl acetate, and dried at
100 ◦ C in vacuo resulting in 5b (1.304 g (54%)) as white needles. Rf (CH2 Cl2 :MeOH = 1:1):
0.63; mp: 180 ◦ C; IR = 2933, 1619, 1562, 1516, 1380, 1323, 1292, 1226, 1181, 1156, 1104,
1062, 1035, 1014, 986; 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.10 (s, 3H, CH3 ), 1.18 (s, 3H,
CH3 ), 1.31–1.52 (m, 6H, (CH2 )3 ), 2.14–2.24 (m, 4H, 3-H, NCH2 ), 2.30–2.39 (m, 2H, NCH2 ),
4.46 (s, 1H, 1′ -H), 6.96 (d, J = 6.8 Hz, 1H, 6-H), 7.44–7.48 (m, 3H, 1-H, ArH), 7.59 (d,
J = 8.1 Hz, 2H, ArH); 13 C NMR (DMSO-d6 , 100 MHz) δ = 24.53 (CH2 ), 26.06 (2CH2 ), 26.16,
26.69 (2CH3 ), 48.81 (C-3), 52.25 (2NCH2 ), 53.09 (C-2), 64.23 (C-1′ ), 105.73 (C-5), 124.64 (q,
1 J(C,F) = 272 Hz, CF ), 125.11 (q, 3 J(C,F) = 3.8 Hz, ArC), 126.70 (q, 2 J(C,F) = 31.6 Hz, ArC ),
q
3
127.91 (ArC), 149.62 (ArCq ), 149.67 (C-6), 188.47 (C-4); HRMS (HESI): calcd. (C20 H26 F3 N2 O+ )
[M]+ : 367.1997; found: 367.1986.
rac-5-[(R)-Cyclohexyl(pyrrolidin-1-yl)methyl]-2,2-dimethyl-2,3-dihydropyridin-4(1H)one (6a) and rac-[(R)-Cyclohexyl(hydroxy)methyl]-2,2-dimethyl-2,3-dihydropyridin-4(1H)one (13): Compound 1a (2.000 g (6.53 mmol)) was suspended in water (30 mL) and KOH
(1.501 g (26.75 mmol)) was added. The mixture was stirred and sonicated at r.t. until most
anything was dissolved. Then, cyclohexane carbaldehyde (0.749 g (6.68 mmol)) was added
and the reaction mixture was stirred for 7 days at r.t. The separated white precipitate
was filtered with suction, washed with water, and dried in vacuo resulting in a white
solid. This was treated with dichloromethane and filtered. The filtrate was evaporated
and the residue crystallized overnight in hot ethyl acetate in the form of sparkling prisms
of 6a (68 mg (4%)). The solid of the dichloromethane filtration was dissolved in hot ethyl
acetate. Overnight, compound 11 (0.355 g (19%)) crystallized as silky needles. Compound
6a: Rf ( CH2 Cl2 :MeOH = 1:1): 0.19; mp: 161 ◦ C; IR (KBr) = 3191, 3023, 2962, 2925, 2849, 2776,
1619, 1585, 1561, 1543, 1409, 1293, 1270, 1241, 1210, 1179; 1 H NMR (DMSO-d6 , 400 MHz)
δ = 0.62–0.78 (m, 2H, CH2 ), 0.95–1.02 (m, 1H, CH2 ), 1.05–1.20 (m, 7H, CH2 , 2CH3 ), 1.52–1.71
(m, 11H, CH, CH2 ), 2.18 (br, s, 2H, 3-H), 2.22–2.26 (m, 2H, NCH2 ), 2.28–2.33 (m, 2H, NCH2 ),
3.23 (d, J = 6.5 Hz, 1H, 1′ -H), 6.95 (d, J = 6.6 Hz, 1H, 6-H), 7.20 (d, J = 6.6 Hz, 1H, 1-H);
13 C NMR (DMSO-d , 100 MHz) δ = 22.99 ((CH ) ), 26.03 (CH ), 26.10 (CH ), 26.26 (CH ),
6
2 2
2
3
2
26.55 (CH3 ), 26.83, 27.79, 31.26 (3CH2 ), 40.45 (CH), 49.13 (C-3), 50.45 (2NCH2 ), 52.78 (C-2),
61.81 (C-1′ ), 103.50 (C-5), 149.44 (C-6), 189.39 (C-4); HRMS (HESI): calcd. (C18 H31 N2 O+ )
[M + H]+ : 291.2436; found: 291.2426.
Crystal Structure Determination of 6a: All the measurements were performed using monochromatized Mo Kα radiation at 100 K: C18 H30 N2 O, Mr 290.44, orthorhombic,
space group P b c a, a = 10.5346(4)Å, b = 11.7374(4)Å, c = 28.1853(11)Å, V = 3485.1(2)Å3 ,
Z = 8, dcalc = 1.107 g cm−3 , µ = 0.068 mm−1 . A total of 125,061 reflections were collected
(Θmax = 30.0◦ ), from which 5084 were unique (Rint = 0.0642), with 4213 having I > 2σ(I). The
structure was solved using direct methods (SHELXS-97) [29] and refined using full-matrix
least-squares techniques against F2 (SHELXL-2014/6) [30]. The non-hydrogen atoms were
refined with an-isotropic displacement parameters without any constraints. The position
of the H atom bonded to N1 was taken from a difference Fourier map, the N–H distance
was fixed to 0.88 Å, and this H atom was refined with an individual isotropic displacement
parameter without any constraints to the bond angles. The H atom bound to C6 was put
at the external bisector of the N–C–C angle at a C–H distance of 0.95 Å and an individual
isotropic displacement parameter was refined for it. The H atoms of the tertiary C–H
groups were refined with individual isotropic displacement parameters and all X–C–H
Molecules 2023, 28, 6869
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angles were equal at a C–H distance of 1.00 Å. The H atoms of the CH2 groups were refined
with common isotropic displacement parameters for the H atoms of the same group and
idealized geometry with approximately tetrahedral angles and C–H distances of 0.99 Å.
The H atoms of the methyl groups were refined with common isotropic displacement
parameters for the H atoms of the same group and idealized geometries with tetrahedral
angles, enabling rotations around the C–C bonds, and C–H distances of 0.98 Å. For the
211 parameters, final R indices of R1 = 0.0431 and wR2 = 0.1167 (GOF = 1.035) were obtained.
The largest peak in a difference Fourier map was 0.417 eÅ−3 . The final atomic parameters,
as well as bond lengths and angles, were deposited at the Cambridge Crystallographic
Data Centre (CCDC 2193723).
Compound 11 from 15:
Compound 15 (0.412 g (3.29 mmol)) was dissolved in a solution of KOH (0.752 g
(13.4 mmol)) in distilled water (15 mL) with sonication. To this solution, cyclohexyl
carbaldehyde (0.375 g (3.24 mmol)) was added and the mixture stirred at r.t. After a few
minutes a white precipitate was formed. To complete the reaction, the mixture was stirred
for a further 4 days at r.t. The white precipitate was sucked off, washed with water, and
dried over phosphorous pentaoxide in a desiccator under reduced pressure. Yield: 0.712 g
(91%) of pure alcohol 11.
Data of compound 11: Rf (CH2 Cl2 :MeOH = 1:1): 0.79; mp: 180 ◦ C; IR = 3283, 3221, 3042,
2926, 2849, 1557, 1519, 1409, 1309, 1264, 1244, 1183, 1121; 1 H NMR (DMSO-d6 , 400 MHz)
δ = 0.79–0.95 (m, 2H, CH2 ), 0.99–1.12 (m, 3H, CH2 ), 1.15 (s, 3H, CH3 ), 1.18 (s, 3H, CH3 ),
1.26–1.35 (m, 1H, CH), 1.42 (br, d, J = 12.9 Hz, 1H, CH2 ), 1.54–1.67 (m, 3H, CH2 ), 1.77
(br, d, J = 13.0 Hz, 1H, CH2 ), 2.11–2.20 (m, 2H, 3-H), 4.07 (dd, J = 6.7, 5.0 Hz, 1H, 1′ -H),
4.21 (d, J = 5.0 Hz, 1H, OH), 7.04 (d, J = 6.6 Hz, 1H, 6-H), 7.28 (d, J = 6.7 Hz, 1H, 1-H);
13 C NMR (DMSO-d , 100 MHz) δ = 26.02 (CH ), 26.04 (CH ), 26.16 (CH ), 26.56 (CH ),
6
2
3
2
2
26.92 (CH3 ), 28.63, 29.33 (2CH2 ), 44.23 (CH), 49.17 (C-3), 52.90 (C-2), 70.05 (C-1′ ), 109.10
(C-5), 148.23 (C-6), 188.81 (C-4); HRMS (HESI): calcd. (C14 H22 NO2 − ) [M − H]− : 236.1651;
found: 236.1658.
rac-5-[(R)-Cyclohexyl(piperidin-1-yl)methyl]-2,2-dimethyl-2,3-dihydropyridin-4(1H)one (6b): Compound 1b (2.091 g (6.53 mmol)) was suspended in water (30 mL) and KOH
(1.449 g (25.82 mmol)) was added. The mixture was stirred and sonicated at r.t. until
most anything was dissolved. Then, cyclohexane carbaldehyde (0.749 g (6.68 mmol)) was
added and the reaction mixture was stirred for 7 days at r.t. The separated off-white solid
was filtered with suction, washed with water, and dried in vacuo. It was treated with
dichloromethane and the suspension was filtered. The filtrate was evaporated and the
residue dissolved in hot ethyl acetate. After the first crystallization, a solid mixture was
sucked off. From the filtrate, 6b crystallized as yellowish prisms (0.170 g (9%)). The solid
from the treatment with dichloromethane was dissolved in the minimum amount of hot
ethyl acetate and left for crystallization overnight. The solid was sucked off and dried
yielding 11 (0.355 mg (23%)) as white needles. Compound 6b: Rf (CH2 Cl2 :MeOH = 1:1):
0.84; mp: 154 ◦ C; IR = 3203, 3026, 2927, 2848, 1616, 1562, 1397, 1383, 1293, 1276, 1259,
1242; 1 H NMR (DMSO-d6 , 400 MHz) δ = 0.57–0.66 (m, 1H, CH2 ), 0.74–0.84 (m, 1H, CH2 ),
1.00–1.16 (m, 3H, CH2 ), 1.18, 1.19 (2s, 6H, 2CH3 ), 1.22–1.75 (m, 11H, CH, CH2 ), 1.92–2.00
(m, 1H, CH2 ), 2.00–2.09 (m, 2H, NCH2 ), 2.19 (s, 2H, 3-H), 2.22–2.29 (m, 2H, NCH2 ), 3.14 (br,
s, 1H, 1′ -H), 6.90 (d, J = 6.6 Hz, 1H, 6-H), 7.18 (d, J = 6.6 Hz, 1H, 1-H); 13 C NMR (DMSO-d6 ,
100 MHz) δ = 24.95 (CH2 ), 25.84 (CH3 ), 25.96, 26.03 (2CH2 ), 26.35 (2CH2 ), 26.65 (CH3 ), 26.78,
30.50, 31.33 (3CH2 ), 36.58 (CH), 49.14 (C-3), 50.24 (2NCH2 ), 52.77 (C-2), 64.45 (C-1′ ), 101.84
(C-5), 148.69 (C-6), 190.15 (C-4); HRMS (HESI): calcd. (C14 H22 NO+ ) [M + H − C5 H11 N]+ :
220.1701; found: 220.1693.
rac-2,2-Dimethyl-5-[(R)-(4-methylphenyl)(pyrrolidin-1-yl)methyl]-2,3-dihydropyridin4(1H)-one (7a): Compound 1a (1.000 g (3.27 mmol)) was suspended in water (16 mL) and
KOH (0.733 g (13.1 mmol)) was added. The mixture was stirred at r.t. until a solution was
formed (ca. 5–10 min). Then, 4-methylbenzaldehyde (0.393 g (3.27 mmol)) was added and
the reaction mixture was stirred for 6 days at r.t. The separated beige crystalline solid was
Molecules 2023, 28, 6869
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filtered with suction, washed with water, and dried in vacuo over phosphorus pentoxide. It
was treated with hot ethyl acetate. The insoluble parts were removed via filtration and the
filtrate was concentrated in vacuo. Crystallization took place overnight yielding 7a (0.440 g
(45%)) as colorless plates. Rf (CH2 Cl2 :MeOH = 1:1): 0.25; mp: 167 ◦ C; IR = 3240, 2968, 1622,
1571, 1536, 1394, 1240; 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.07 (s, 3H, CH3 ), 1.16 (s, 3H,
CH3 ), 1.57–1.67 (m, 4H, (CH2 )2 ), 2.09–2.17 (m, 2H, 3-H), 2.22 (s, 3H, ArCH3 ), 2.24–2.40 (m,
4H, 2NCH2 ), 4.27 (s, 1H, 1′ -H), 7.02 (d, J = 7.8 Hz, 2H, ArH), 7.08 (d, J = 6.8 Hz, 1H, 6-H),
7.13 (d, J = 7.8 Hz, 2H, ArH), 7.30 (d, J = 6.8 Hz, 1H, 1-H); 13 C NMR (DMSO-d6 , 100 MHz)
δ = 20.79 (ArCH3 ), 23.35 ((CH2 )2 ), 26.04, 26.92 (2CH3 ), 48.98 (C-3), 52.81 (2NCH2 ), 53.01
(C-2), 63.58 (C-1′ ), 109.27 (C-5), 126.91, 128.69 (ArC), 134.90, 142.63 (ArCq ), 149.13 (C-6),
187.83 (C-4); HRMS (HESI): calcd. (C19 H27 N2 O+ ) [M + H]+ : 299.2123; found: 299.2116.
rac-5-[(R)-(4-Isopropylphenyl)(pyrrolidin-1-yl)methyl]-2,2-dimethyl-2,3dihydropyridin-4(1H)-one (8a): Compound 1a (2.000 g (6.53 mmol)) was suspended in
water (32 mL) and KOH (1.466 g (26.13 mmol)) was added. The mixture was stirred at
r.t. until a solution was formed (ca. 5–10 min). Then, 4-isopropylbenzaldehyde (0.968 g
(6.53 mmol)) was added and the reaction mixture was stirred for 5 days at r.t. The separated
resinous beige product was dried in vacuo over phosphorus pentoxide and then treated
with hot ethyl acetate. The insoluble part was filtered off. Cyclohexane was added to the
solution and the mixture was allowed to stand overnight. The precipitate was filtered
off and discarded, the filtrate was evaporated to dryness, and the residue was recrystallized from ethyl acetate resulting in an almost pure product. Further crystallization from
ethyl acetate afforded pure 8a (0.118 g (6%)) as white needles. Rf (CH2 Cl2 :MeOH = 1:1):
0.91; mp: 152 ◦ C; IR = 3240, 3042, 2963, 1622, 1568, 1461, 1395, 1290, 1239, 1181; 1 H NMR
(DMSO-d6 , 400 MHz) δ = 1.09 (s, 3H, CH3 ), 1.15–1.16 (m, 9H, CH(CH3 )2 , CH3 ), 1.61–1.65
(m, 4H, (CH2 )2 ), 2.14 (s, 2H, 3-H), 2.25–2.37 (m, 4H, 2NCH2 ), 2.80 (quin, J = 6.9 Hz, 1H,
CH(CH3 )2 ), 4.28 (s, 1H, 1′ -H), 7.07–7.09 (m, 3H, 6-H, 2ArH), 7.16 (d, J = 8.0 Hz, 2H, 2ArH),
7.31 (d, J = 6.7 Hz, 1H, 1-H); 13 C NMR (DMSO-d6 , 100 MHz) δ = 23.33 ((CH2 )2 ), 24.09, 24.12
(CH(CH3 )2 ), 25.94, 27.10 (2CH3 ), 33.16 (CH(CH3 )2 ), 48.95 (C-3), 52.86 (2NCH2 ), 53.02 (C-2),
63.50 (C-1′ ), 109.23 (C-5), 125.99, 126.90 (4ArC), 142.98, 145.90 (ArCq ), 149.23 (C-6), 187.84
(C-4); HRMS (HESI+ ): calcd. (C21 H31 N2 O+ ) [M + H]+ : 327.2436; found: 327.2426.
rac-2,2-Dimethyl-5-[(R)-pyrrolid-4-yl)(pyrrolidine-1-yl)methyl]-2,3-dihydropyridin4(1H)-one (9a): Compound 1a (2.000 g (6.53 mmol)) was suspended in water (32 mL)
and KOH (1.466 g (26.13 mmol)) was added. The mixture was stirred at r.t. until a solution
was formed (ca. 5–10 min). Then, pyridine-4-carbaldehyde (0.700 g (6.53 mmol)) was added
and the reaction mixture was stirred for 4 days at r.t. The solution was extracted 5 times
with dichloromethane and the combined organic layers were dried over sodium sulfate,
filtered, and the solvents evaporated in vacuo resulting in a yellow oil. This was dissolved
in hot ethyl acetate and cooled to r.t. Then, cyclohexane was added dropwise until the
mixture was opacified permanently. After stirring overnight at r.t., the formed precipitate
was sucked off and dissolved in hot ethyl acetate, filtered from insoluble parts, and left for
crystallization yielding 9a (0.170 g (9%)) as yellowish needles. Rf (CH2 Cl2 :MeOH = 1:1):
0.37; mp: 169 ◦ C; IR = 3270, 3026, 2800, 1624, 1594, 1574, 1505, 1386, 1292, 1226, 1180,
1115; 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.07 (s, 3H, CH3 ), 1.16 (s, 3H, CH3 ), 1.64–1.67
(m, 4H, (CH2 )2 ), 2.16 (s, 2H, 3-H), 2.28–2.50 (m, 4H, 2NCH2 ), 4.33 (s, 1H, 1′ -H), 7.10 (d,
J = 6.8 Hz, 1H, 6-H), 7.24 (dd, J = 4.5, 1.6 Hz, 2H, ArH), 7.49 (d, J = 6.8 Hz, 1H, 1-H), 8.40
(dd, J = 4.5, 1.6 Hz, 2H, ArH); 13 C NMR (DMSO-d6 , 100 MHz) δ = 23.34 ((CH2 )2 ), 26.01,
26.76 (2CH3 ), 48.76 (C-3), 52.56 (2NCH2 ), 53.08 (C-2), 63.14 (C-1′ ), 107.57 (C-5), 122.24 (ArC),
149.49, 149.57 (C-6, ArC), 154.17 (ArCq ), 187.77 (C-4); HRMS (HESI): calcd. (C17 H24 N3 O+ )
[M + H]+ : 286.1919; found: 286.1909.
rac-2,2-Dimethyl-5-[(R)-2-methyl-1-(pyrrolidin-1-yl)propyl]-2,3-dihydropyridin-4(1H)one (10a): Compound 1a (2.000 g (6.53 mmol)) was suspended in water (30 mL) and
KOH (1.473 g (26.25 mmol)) was added. To the mixture, isobutyric aldehyde (475 mg
(6.59 mmol)) was added and it was stirred and sonicated at r.t. until nearly all was dissolved. The reaction mixture was stirred for 7 days at r.t. The raw product contained small
Molecules 2023, 28, 6869
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amounts of Morita–Baylis–Hillman product, which was not isolated. The separated red oil
was exhaustively extracted with dichloromethane, and then the combined organic layers
were dried over sodium sulfate, filtered, and the solvent was evaporated in vacuo resulting
in a red oil. This was dissolved in the minimum amount of hot dichloromethane. The
product crystallized in the form of yellowish needles overnight, and then was sucked off
and dried. Yield: 0.255 g (16%). Rf (CH2 Cl2 :MeOH = 1:1): 0.14; mp: 148 ◦ C; IR = 2955,
2771, 1617, 1584, 1562, 1537, 1456, 1408, 1382, 1364, 1268, 1239, 1211, 1181, 1125, 1110, 667;
1 H NMR (DMSO-d , 400 MHz) δ = 0.67 (d, J = 6.6 Hz, 3H, CH(CH ) ), 0.73 (d, J = 6.6 Hz,
6
3 2
3H, CH(CH3 )2 ), 1.17 (s, 3H, CH3 ), 1.18 (s, 3H, CH3 ), 1.52–1.64 (m, 4H, 2CH2 ), 1.94 (dsept,
J = 6.6 Hz, 1H, CH(CH3 )2 ), 2.14–2.23 (m, 2H, 3-H), 2.22–2.36 (m, 4H, 2NCH2 ), 3.18 (d,
J = 6.3 Hz, 1H, 1‘-H), 6.98 (d, J = 6.7 Hz, 1H, 6-H), 7.24 (d, J = 6.7 Hz, 1H, 1-H); 13 C NMR
(DMSO-d6 , 100 MHz) δ = 17.21 (CH(CH3 )2 ), 20.83 (CH(CH3 )2 ), 23.05 (2CH2 ), 25.90, 26.72
(2CH3 ), 30.12 (CH(CH3 )2 ), 49.12 (C-3), 50.84 (2NCH2 ), 52.75 (C-2), 62.71 (C-1‘), 103.16
(C-5), 149.56 (C-6), 189.34 (C-4); HRMS (HESI): calcd. (C15 H27 N2 O+ ) [M + H]+ : 251.2118;
found: 251.2114.
rac-2,2-Dimethyl-5-[(R)-(1-Hydroxy-2,2-dimethylpropyl)-2,3-dihydropyridin-4(1H)one (12): Compound 1a (2.413 g (7.88 mmol)) was suspended in water (32 mL) and KOH
(1.496 g (26.66 mmol)) was added. Then, pivalaldehyde (0.678 g (7.88 mmol)) was added to
the mixture. The reaction mixture was stirred for 4 days at r.t. The formed white fluffy solid
was sucked off and dried overnight in a desiccator over phosphorous pentaoxide. Yield:
1.129 g (68%) Rf (CH2 Cl2 :MeOH = 1:1): 0.80; mp: 168 ◦ C; IR = 3249, 2950, 1526, 1402, 1389,
1366, 1258, 1239, 1211, 1177, 1000; 1 H NMR (DMSO-d6 , 400 MHz) δ = 0.75 (s, 9H, 3CH3 ),
1.16 (s, 3H, CH3 ), 1.20 (s, 3H, CH3 ), 2.12 (d, J = 16.0 Hz, 1H, 3-H), 2.19 (d, J = 16.0 Hz, 1H,
3-H), 4.15 (d, J = 4.6 Hz, 1H, 1′ -H), 4.43 (d, J = 4.8 Hz, 1H, OH), 7.07 (d, J = 6.6 Hz, 1H, 6-H),
7.39 (d, J = 6.8 Hz, 1H, 1-H); 13 C NMR (DMSO-d6 , 100 MHz) δ = 25.45 (CH3 ), 26.13 (3CH3 ),
27.23 (CH3 ), 36.55 (C(CH3 )3 ), 49.11 (C-3), 52.62 (C-2), 72.25 (C-1′ ), 107.94 (C-5), 149.17 (C-6),
188.70 (C-4); HRMS (DIP EI): calcd. (C12 H21 NO2 ) [M+ ]: 211.1567; found: 211.1573.
5,5’-[(4-Ethoxy-3-methoxyphenyl)methylene]bis(2,2-dimethyl-2,3-dihydropyridin4(1H)-one) (13): From 1a: Compound 1a (2.000 g (6.53 mmol)) was suspended in water
(15 mL) and ethanol (30 mL). Then, a solution of KOH (1.488 mg (26.52 mmol)) in a mixture
of water (15 mL) and ethanol (30 mL) was added. Finally, 4-ethoxy-3-methoxybenzaldehyde
(1.177 g (6.53 mmol)) was added and the reaction mixture was stirred for 5 days. Most
of the ethanol was evaporated in vacuo. The remaining solution was diluted with water,
transferred into a separatory funnel, and then extracted 4 times with dichloromethane.
The combined organic layers were dried over sodium sulfate, filtered, and the solvent
was evaporated yielding a yellow oil. This was dissolved in a minimum amount of hot
ethyl acetate. Then, cyclohexane was added dropwise until the mixture was opacified
permanently. The formed beige precipitate was sucked off, washed with a cold mixture
of cyclohexane and ethyl acetate, and dried at 100 ◦ C at reduced pressure resulting in 11
(0.375 g (28%)). For analytical purposes, it was recrystallized from ethyl acetate giving the
product an off-white precipitate.
From 1b: Compound 1b (2.091 g (6.53 mmol)) was suspended in water (15 mL) and
ethanol (30 mL). Then, a solution of KOH (1.579 g (28.14 mmol)) in a mixture of water
(15 mL) and ethanol (30 mL) was added. Finally, 4-ethoxy-3-methoxybenzaldehyde (1.177 g
(6.53 mmol)) was added and the reaction mixture was stirred for 5 days. Most of the ethanol
was evaporated in vacuo. The remaining solution was diluted with water, transferred into a
separatory funnel, and then extracted 4 times with dichloromethane. The combined organic
layers were dried over sodium sulfate, filtered, and the solvent was evaporated resulting in
a yellow oil. This oil was dissolved in a minimum amount of hot ethyl acetate. Cyclohexane
was added dropwise until the mixture was opacified permanently. The formed beige
precipitate was sucked off, washed with a cold mixture of cyclohexane and ethyl acetate,
and dried at 100 ◦ C at reduced pressure resulting in 13 (0.830 g (62%)). For analytical
purposes, it was recrystallized from ethyl acetate resulting in the product as an off-white
precipitate. Rf (CH2 Cl2 :MeOH = 1:1): 0.80; mp: 125 ◦ C; IR = 2968, 1578, 1512, 1378, 1294,
Molecules 2023, 28, 6869
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1241, 1182, 1135; 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.17 (s, 6H, 2CH3 ), 1.18 (s, 6H, 2CH3 ),
1.28 (t, J = 7.0 Hz, 3H, OCH2 CH3 ), 2.14–2.22 (m, 4H, 3-H, 3′ -H), 3.65 (s, 3H, OCH3 ), 3.92 (q,
J = 7.0 Hz, 2H, OCH2 CH3 ), 4.84 (s, 1H, CH), 6.50 (dd, J = 8.5, 2.0 Hz, 1H, ArH), 6.55–6.62
(m, 3H, 6-H, 6′ -H, ArH), 6.78 (d, J = 8.2 Hz, 1H, ArH), 6.99 (d, J = 6.7 Hz, 2H, 1-H, 1′ -H); 13 C
NMR (DMSO-d6 , 100 MHz) δ = 15.08 (OCH2 CH3 ), 26.36, 26.80 (4CH3 ), 37.99 (CH), 49.35
(C-3, C-3′ ), 53.12 (C-2, C-2′ ), 55.42 (OCH3 ), 63.90 (OCH2 ), 109.22 (C-5, C-5′ ), 112.38, 112.89,
119.87 (ArC), 138.27, 145.83, 148.65 (ArCq ), 148.81 (C-6, C-6′ ), 188.74 (C-4, C-4′ ); HRMS
(HESI): calcd. (C24 H33 N2 O4 + ) [M + H]+ : 413.2440; found: 413.2433.
5,5’-(Ferrocenylmethylene)bis(2,2-dimethyl-2,3-dihydropyridin-4(1H)-one) (14): Compound 1a (2.000 g (6.53 mmol)) was suspended in water (15 mL) and ethanol (30 mL).
Then, a solution of KOH (1.435 g (25.57 mmol)) in a mixture of water (15 mL) and ethanol
(30 mL) was added. Finally, ferrocene carbaldehyde (1.398 g (6.53 mmol)) was added. The
reaction mixture was stirred for 5 days. The formed precipitate was sucked off and dried in
vacuo over phosphorus pentoxide. It was treated with hot ethyl acetate and filtered. The
filtrate was discarded. The precipitate was suspended in a mixture of dichloromethane
and ethanol (4:1) and filtered off. Then, the filtrate was evaporated and the residue was
dissolved in a hot mixture of ethyl acetate and ethanol (1:1). The mixture was filtered and
the filtrate was left for crystallization overnight. The formed solid was sucked off and dried
at 150 ◦ C in vacuo resulting in 14 (0.850 g (58%)) as a yellow solid. Rf (CH2 Cl2 :MeOH = 1:1):
0.83; mp: 262 ◦ C (decomp.); IR = 3441, 3288, 2965, 1620, 1569, 1528, 1382, 1297, 1243, 1177;
1 H NMR (DMSO-d , 400 MHz) δ = 1.14 (s, 6H, 2CH ), 1.17 (s, 6H, 2CH ), 2.09–2.18 (m, 4H,
6
3
3
3-H, 3′ -H), 3.85 (br, s, 2H, ArH), 4.01 (br, s, 2H, ArH), 4.07 (s, 5H, ArH), 4.63 (s, 1H, CH),
6.80 (d, J = 6.7 Hz, 2H, 6-H, 6′ -H), 6.92 (d, J = 6.7 Hz, 2H, 1-H, 1′ -H); 13 C NMR (DMSO-d6 ,
100 MHz) δ = 26.32, 26.48 (4CH3 ), 32.76 (CH), 49.49 (C-3, C-3′ ), 53.01 (C-2, C-2′ ), 66.50
(2ArC), 68.01 (2ArC), 68.41 (5ArC), 94.48 (ArCq ), 110.75 (C-5, C-5′ ), 148.78 (C-6, C-6′ ), 188.07
(C-4, C-4′ ); HRMS (HESI): calcd. (C25 H31 FeN2 O2 + ) [M + H]+ : 447.1735; found: 447.1721.
2,2-Dimethyl-2,3-dihydropyridin-4(1H)-one (15): Compound 1b (2.50 g (7.81 mmol))
was suspended in 37.5 mL water and KOH (2.127g (37.91 mmol)) was added. The mixture
was stirred at r.t. for 4 days. The solution was transferred into a separatory funnel
and extracted 10 times with dichloromethane. The combined organic phases were dried
over sodium sulfate, filtered, and the solvent evaporated. The remaining oil crystallized
spontaneously resulting in 15 as an off-white solid. Yield: 812 mg (6.49 mmol; 83%). The
melting point (93◦ ) corresponds well with that reported (93–94◦ ) by Gusev [9] for this
compound. 1 H NMR (DMSO-d6 , 400 MHz) δ = 1.17 (s, 6H, 2CH3 ), 2.16 (br, s, 2H, 3-H), 4.62
(dd, J = 7.1, 1.2 Hz, 1H, 5-H), 7.13 (dd, J = 7.0, 6.9 Hz, 1H, 6-H), 7.41 (br, s, 1H, 1-H); 13 C
NMR (DMSO-d6 , 100 MHz) δ = 26.36 (2CH3 ), 49.25 (C-3), 53.01 (C-2), 95.00 (C-5), 150.22
(C-6), 190.60 (C-4).
3.3. Bioassays
3.3.1. Cytotoxicity against Human (Cancer) Cell Lines
The human leukemia cell line CCRF-CEM was cultured in RPMI 1640 medium
containing 2 mM of L-glutamine (Gibco® , Thermo Fisher Scientific Inc., Waltham, MA,
USA) supplemented with 10% fetal bovine serum (FBS), 100 units/mL of penicillin, and
100 µg/mL of streptomycin (all obtained from Gibco® ). Human MRC-5 lung fibroblasts were cultivated in Minimum Essential Medium (MEM; Gibco® ) containing 4 mM of
L-glutamine, 10% of FBS, 100 units/mL of penicillin, and 100 µg/mL of streptomycin. MRC5 cells were sub-cultured at 90% confluence via trypsinization using a 0.25% trypsin-EDTA
solution (Gibco® ).
Cytotoxicity was measured via cell metabolic activity, which was determined using
XTT (2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide). Cells in
the logarithmic growth phase were seeded into 96-well plates (flat bottom; 100 µL/well) at
a density of 10,000 cells/well. CCRF-CEM cells were immediately used for experiments,
whereas MRC-5 cells were incubated overnight before being used for experiments. Both
cell lines were treated with compounds (5 and 50 µM) for 72 h before cell metabolic activity
Molecules 2023, 28, 6869
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was determined using a commercial kit (Cell proliferation kit II, Roche) according to the
manufacturer’s instructions. CCRF-CEM and MRC-5 cells were incubated with the XTT
solution for 4 h and 2 h, respectively. Then, absorbance was measured at 490 nm using
a Hidex Sense microplate reader (Hidex, Turku, Finland). Experiments were performed
as two independent experiments carried out in triplicates. Cell viability was calculated
relative to mock-treated cells (0.1% DMSO) using blank-corrected values. Vinblastine
(100 nM) served as a positive control.
3.3.2. Antibacterial Activity
All compounds were dissolved in DMSO at a concentration of 0.01 mg/µL and the
disc plate method [31] was used to detect bioactivity against Gram-positive (B. subtilis)
and Gram-negative (E. coli) bacteria. The results were noted as the ability of the compound to inhibit the growth of the corresponding test organism by noting the zone of
inhibition (ZOI) around a disc (6 mm) as follows: mild clearance = detectable activity (±)
(ZOI = 7–9 mm), clearance = active (+) (ZOI = 10 mm), and clear clearance = higher activity
(++) (ZOI > 10 mm). Compound 6a has cyclohexane moiety that could have interfered with
its ability to penetrate the bacterial outer membrane (lipopolysaccharide layer), disrupting
this layer that is structurally significant in Gram-negative bacteria [32], while the addition
of fluorine improved Gram-negative activity in 3a, 4b, 5a, 5b. Fluorine has the ability to
change the electron distribution of a molecule, leading to modifications in the molecule’s
pKa, dipole moment, chemical reactivity, and stability. The introduction of fluorine can
reduce the basicity of compounds, resulting in improved bioavailability as a result of better
permeation via cellular membranes.
4. Conclusions
Exposition of 4-amino-tetrahydropyridinylidene salts to a series of aldehydes in
an alkaline medium afforded 5-substituted dihydropyridin-4(1H)-ones. The expected
β-hydroxyketone was only isolated after reaction with cyclohexane carbaldehyde. Aromatic aldehydes were yielded in most cases β-aminoketones and less frequently δ-diketones.
Most of the aminoketones exhibited anti-proliferative activity against human leukemia cells.
A few of these compounds showed high inhibitory activity against Escherichia coli, whereas
the β-hydroxyketone was the most active against Bacillus subtilis. These compounds could
be a base for further investigation in order to produce leading compounds that could be
further refined and optimized for possible applications.
Supplementary Materials: The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/molecules28196869/s1. Figures S1–S21: 1H-, 13C-NMR, and
MS-spectra. Tables S1–S7: Crystal data.
Author Contributions: Conceptualization, W.S. and M.H.; investigation, W.S., M.H., F.B., T.P., M.A.,
E.-M.P.-W., R.S. and R.W.; methodology W.S. and M.H.; data curation, W.S., M.H., F.B., T.P., M.A.,
E.-M.P.-W. and R.S.; writing—original draft preparation, W.S. and R.W.; writing—review and editing,
W.S., E.-M.P.-W., T.P., R.B. and R.W.; supervision, W.S. and R.B.; project administration, W.S. All
authors have read and agreed to the published version of the manuscript.
Funding: Open access funding by the University of Graz.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available in this article.
Acknowledgments: The authors acknowledge open access funding by the University of Graz. Furthermore, NAWI Graz is acknowledged for supporting the Graz Central Lab Environmental, Plant &
Microbial Metabolomics. Support from the “Jeol Application Lab” at Graz University of Technology
is gratefully acknowledged.
Conflicts of Interest: The authors declare no conflict of interest.
Molecules 2023, 28, 6869
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Sample Availability: Samples of selected compounds are available from the authors.
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